In automobiles equipped with an air bag, a sensor perceives shock upon collision and operates to generate gas of high temperature and high pressure. Then, the air bag is instantly developed by the gas whereby human bodies or, particularly, faces and foreheads heads of a driver and a passenger are protected during collision. In recent years, an air bag for automobiles has been widely diffused as one of safety equipments and there has been a progress in its practical utilizations not only for seats for a driver's seat and a passenger seat but also for knee bag, side bag, curtain air bag, etc. Accordingly, automobiles in which a plurality of air bags are installed as a standard equipment have been increasing.
As regions and numbers of the installed air bags are increasing, there has been an increasing demand for making weight and size of an air bag system lighter and more compact and, each of the parts of the system has been designed with a target of making its weight lighter and its size more compact. As a result of such a background, a bag body for an air bag has been also investigated for making its weight light by means of reducing a bag volume and of making the base fabric to be used therefor non-coating.
There are many kinds of types for an inflator which inflates an air bag. In such a view that making its size and weight small and light, respectively is possible, use of a pyro-inflator has been rapidly increasing in recent years. However, the pyro-inflator has such a characteristic that incompletely combusted components generated from a gas generator and floating fine particles due to the residue after combustion of explosives are too much whereby the thermal affection thereby to an air bag tends to be big. With regard to a base fabric used for main body of an air bag, it goes without saying that there is a demand for high heat resistance. In addition, with regard to a heat-resistant reinforcing fabric used for an inflator attachment port, there is also a demand for high heat resistance.
Up to now, waste pieces after cutting a fabric for main body of an airbag have been used as a reinforcing fabric. However, as the weight of a fabric for the main body becomes light, heat resistance of the fabric for the main body lowers and, for compensating it, it has been necessary to increase the numbers of the reinforcing fabrics. The increase in the numbers of the reinforcing fabrics leads to complicated sewing and accordingly increase in the mass of the whole airbag. In view of these inconveniences, there has been a demand for a base fabric which can resist to thermal damage even if its using numbers are decreased.
Up to now, there has been used a coated fabric wherein a heat-resistant elastomer such as chloroprene rubber or silicone rubber is adhered to a woven fabric in an amount of 60 to 120 g/m2 so as to resist to high-temperature gas which is instantly gushed from an inflator. Moreover, there has been also investigated a base fabric for an air bag wherein application liquid of elastomer resin is applied for plural times so as to form a plurality of layers, and wherein the total applied amount in terms of the elastomer resin is made 100 to 400 g/m2 (for example, see Patent Document 1).
However, since the applied amount for this coated fabric is very much, although it is excellent in its heat resistance, the mass of the whole coated fabric increases and that is not preferred in view of making the weight light. In addition, the applied layer becomes hard and that is not preferred in terms of its storage as well. Moreover, when the applied amount is too much, there has been a problem of an increase in tackiness due to contact between the coat surfaces.
On the other hand, there have been investigated a base fabric for an air bag and also an air bag which use a non-coated base fabric for an air bag exhibiting excellent light weight and storing ability and which suppresses hole formation by high-temperature mist generated from an inflator (for example, see Patent Document 2).
To be more specific, the Patent Document 2 discloses a woven fabric having excellent resistance to melting wherein hole formation of a test piece by an anti-melting test is in grade two or higher. This fabric uses a single yarn having flat cross section and uses a synthetic fiber multifilament having total fineness of 400 to 700 dtex. In the above-mentioned anti-melting test, evaluation was conducted by placing a sample on a hot iron of 350° C. for five seconds. In this evaluating method however, there is a problem that the degree of heat-resistance property cannot be shown clearly in such a respect that a heated thing of high temperature is applied to a fabric for long time, as compared with the evaluating result for an air bag which actually uses an inflator gas of high temperature. Since a base fabric for an air bag is designed using an evaluating method having insufficient differentiation as such, a base fabric for an air bag prepared in the Patent Document 2 cannot be said to be sufficient in terms of heat resistance.